the welded seam shape of ERW steel pipe

ERW steel pipe welding technology adopts skin effect principle produced by high frequency current to heat hot rolled coil to molten state, then through the mechanical extrusion method to weld. Adopting this welding technology, ERW pipe welding seam center will have a white fusion line, and the heat affected zone on both sides of the fusion line will produce metal flow from the central to the extension direction to the surface. During the welding process, tube metal will round the heat cycle process cold, hot and cold again. So, parent metal physic-chemical properties, grain size and non-metallic inclusion as well as forming and welding conditions and heat treatment process will have an impact on the performance of the welded seam especially impact toughness. In the process of ERW steel tubes, choosing the impact toughness of the plates ensure the performance of welded steel pipes, combination of control and adjustment of the welding process ensure to reduce defects as far as possible and improve the weld seam performance.

ERW Steel Pipe/Tubes
ERW steel tubes

Welding quality of welded seam can be achieved by the appearance like welded seam shape, surface condition and mechanical properties of welded seam inspection and metallographic analysis to decide. In the process of production, welded seam shape of bending form and surface condition can provide the reference for the welding process adjustment. Mechanical properties testing are generally carried out in accordance with the standards or customers’ special requirements.

Welded Seam Quality and Welded Seam Surface Shape

A variety of quality defects are caused by many factors in the welded pipe production. But welded seam quality problems are mainly caused by both inside and outside temperature difference of the steel plate’s edge and pressure and heating unmatched.

Steel Plate Boundary Temperature Difference and Surface Shape

Inside and outside edge temperature inconsistent cannot exceed the scope; otherwise it will cause serious quality problems for ERW steel tubes. One of the typical two extreme problems are burnt and cold welding. Burnt is to ensure the inside and outside “fusion” and make one side high temperature “burnt”. When remove the burr, we can found the oxide and impurities staying on this side which form visible welding cracks and holes. Or in order to limit the lateral temperature beyond a certain range will lead to cold weld on the other side. When temperature difference is not beyond the scope completely, the welding quality is judged by examining.

Cooperation Between Heating Temperature and Surface Morphology

Whether appropriate between squeeze and heating temperature will eventually influence welding seam joint surface strength and appearance. Generally, the extrusion quantity have a proper range, when lager extrusion, reduce heating temperature properly; when smaller extrusion, increase heating temperature appropriately. This will guarantee welding strength and welded seam shape to achieve good comprehensive effect.

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